Why should I buy Premium Potting Media?

As a student at Burnley through the mid eighties and starting a nursery career immediately afterwards I was aware of strongly held views over the merits or otherwise of potting mix.  When I look back now I realise that a technological development was in the process of dramatically changing our industry.  The development of modern potting media, the origins of which can be traced back to ancient Egyptian times has some valuable lessons for both nurserymen and gardeners.  How and why did we transition from growing plants in soil to today’s completely soil-less potting media?

My Grandfather, David Wood started working for Fred Linton in 1932.  Dave was only 17 and Fred not much older.  They grew cut flowers in the sandy soil of the Scotsburn Estate in South Oakleigh; Violets, Daphne, Polyanthus, Delphinium and Poppies bunched with gum tips from the surrounding scrub.  Other nurseries were selling bare rooted deciduous trees or field grown trees & shrubs “balled and burlapped”.  Despite a history of plants being grown in containers dating back to the Egyptians and evidence of ceramic pots being used by both the Romans and the Chinese, what we now call the “container growing” industry was still in its infancy in the 1930’s.

Nobody remembers what prompted Fred and Dave to start growing and selling plants in pots.  It’s a fair bet that they were not the first, although over a long career Fred proved to be quite an innovator.  It’s also something of a guess that they started by “lifting” field grown plants and transferring them to pots which led to the idea of growing in the container itself.  As “seedling growers” Fred & Dave used a cut down timber fruit case as their container, others were using assorted tin cans, tar paper and terra cotta pots.  But the pot is just a means of transport, what were the plants actually growing in?  Sandy soil.  If plants came down from the hills, red mountain soil.

The prime differentiating factor for growers was and in many ways remains their “secret recipe”.
Early media recipes adapted and modified the base soil ingredient.  Sand, leaf mould, ash, peat were all added to help open heavy soils or provide moisture retention to sandy soils.  Nutrition came from the original source, manure.  Regular trips to Wirth’s permanent Circus site on what is now the Arts Centre, Melbourne reaped a rich reward of Elephant, Camel, Horse and other manures.  My Uncle Robert’s job as a school boy was to “fill the trays”: line the tray with newspaper, add an inch thick layer of manure and finish with a layer of top soil.  The top soil was just that, soil collected from the housing developments springing up all around Melbourne following WWII.

These mixes had two particular problems.  1.  The source materials varied in the level of nutrient they carried so there was no way of controlling weather there was too much or too little for the plants.  And 2. Infestation. With soil from a wide range of sources making the primary component of these mixes controlling the pests, weeds and diseases that came with them became the primary concern.

The John Innes Horticultural Research Institute (UK) developed a series of standard soil blends in the 1930’s.  Using the base materials of loam (soil), sand and peat the Innes blends introduced the concept of heat treatment to kill off the various pests, weeds & diseases.  Steam pasteurization was recommended as the ideal but the modified version at Fred Linton’s was cooking the soil on a sheet of steel over a fire pit.  John Innes composts still have a loyal following, particularly in the UK.  The argument is that loam is natural and offers natural tolerance to environmental variations.  Natural earth certainly does have a much greater capacity to protect plants from environmental extremes than plants growing in small containers, but I personally think this has more to do with the volume of media than properties inherent to soil.  Another concern with the use of loam (topsoil) as the primary ingredient of potting media is that loam is actually a scarce and valuable natural resource.  Over time topsoil became relatively very expensive and while heat treatment solved some of the pest and disease issues it was far from completely effective.  

Enough for now, I'll print a little more next week.